U.S. patent number 5,581,246 [Application Number 07/840,933] was granted by the patent office on 1996-12-03 for multiple device control system.
This patent grant is currently assigned to Gulton Industries, Inc.. Invention is credited to David M. Albert, James K. Alexanderson, Robert E. Rector, Larry T. Taylor, Scott H. Yarberry.
United States Patent |
5,581,246 |
Yarberry , et al. |
* December 3, 1996 |
Multiple device control system
Abstract
A train communication and control system is described having the
cars of the train connected by a two-wire train line running
continuously from car to car. Each car has a transmitting circuit
and a receiving circuit connected across the line. Any car may be
selected to be a master unit. The selection of one car as a master
unit disconnects the power sources of all other cars from the train
line, leaving the master unit power source as the sole power source
for the line. The master unit or any other car unit communicates
with each other car by causing a high voltage ("mark" state or
logic one) or a low voltage ("space" state or logic zero) to be on
the train line. Each non-master car can receive a communication
from a transmitting circuit, or can transmit to another car by
applying a low impedance across the train line to change from a
"mark" state to a "space" state. The power source consists of a
voltage regulator with precision constant current limit. Output
voltage is maintained substantially constant until a load greater
than the rated current limit causes the power source to change to a
substantially constant current regulator, whereby its regulated
voltage falls rapidly to the "space" state voltage.
Inventors: |
Yarberry; Scott H. (Plano,
TX), Rector; Robert E. (Richardson, TX), Taylor; Larry
T. (Garland, TX), Alexanderson; James K. (Carrollton,
TX), Albert; David M. (Plano, TX) |
Assignee: |
Gulton Industries, Inc. (Plano,
TX)
|
[*] Notice: |
The portion of the term of this patent
subsequent to August 25, 2009 has been disclaimed. |
Family
ID: |
23880549 |
Appl.
No.: |
07/840,933 |
Filed: |
February 25, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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473678 |
Feb 1, 1990 |
5142277 |
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Current U.S.
Class: |
340/6.12; 246/1C;
340/310.11; 340/870.38 |
Current CPC
Class: |
B61L
15/0045 (20130101) |
Current International
Class: |
B61L
15/00 (20060101); H04Q 001/00 () |
Field of
Search: |
;340/825.38,825.06,825.08,31A,505,825.57,870.38 ;370/85.2,85.3,85.4
;343/220 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2302641 |
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Feb 1976 |
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FR |
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2535133 |
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Oct 1982 |
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FR |
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2521388 |
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Nov 1976 |
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DE |
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2558374 |
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Jun 1977 |
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DE |
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3329049 |
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Mar 1984 |
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DE |
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Primary Examiner: Yusko; Donald J.
Assistant Examiner: Zimmerman; Brian
Attorney, Agent or Firm: Darby & Darby, P.C.
Parent Case Text
This is a continuation, of application Ser. No. 473,678, filed Feb.
1, 1990 now U.S. Pat. No. 5,142,277.
Claims
We claim:
1. A communication system comprising
a plurality of spatially separated units, each unit comprising
(a) a communication line section consisting of two continuous
galvanically conductive wires, the line section of each unit being
galvanically serially connected to the line sections of all other
units to form a single two-wire line for all units,
(b) a transmitting circuit, and
(c) a receiving circuit,
each of said transmitting circuits and receiving circuits being
connected in parallel across said line at its respective location
whereby all said circuits are connected directly to said two
wires,
a single direct voltage source connected across said line at only
one point thereof at any one time and providing the only source of
voltage on said line,
each transmitting circuit comprising means for causing the voltage
on said line produced by said voltage source to vary at all points
along said line between a high level and a low level in
correspondence with a binary signal to be transmitted,
all said receiving circuits being adapted to respond to variation
of voltage on said line caused by a transmitting circuit of any one
unit, to reproduce said signal.
2. A system as in claim 1 in which said means for varying voltage
at each transmitting circuit comprises a shunting circuit for
placing a low impedance shunt across said line in correspondence
with said signal.
3. A system as in claim 1, said source including a regulator
providing a regulated voltage output for currents up to the
aggregate standby current drain from all said transmitting and
receiving circuits, and providing a regulated current output for
current drain substantially greater than said standby drain,
said shunt-applying means being operative to provide a current draw
from said regulator to cause said regulator to operate in a
regulated-current mode.
4. A system as in claim 1 wherein said voltage source has the
characteristic of maintaining substantially uniform voltage output
for loads across said line having resistance above a predetermined
value.
5. A system as in claim 1 wherein said voltage source has the
characteristic of maintaining substantially uniform current for
loads across said line having resistance below a predetermined
value.
6. A system as in claim 1 wherein said voltage source has the
characteristic of maintaining substantially uniform voltage output
for loads across said line having resistance above a predetermined
value, and also of maintaining substantially uniform current for
loads across said line having a resistance below a predetermined
value.
7. A message display system comprising
a plurality of units as in claim 1,
a plurality of message display devices,
each of said units being a sign control unit associated with one or
more of said display devices at a respective unit location, said
sign control units being connected to one another solely by said
two-wire line,
each sign control unit also comprising a said voltage source whose
output is coupled across said line, an operator's control, a said
transmitting circuit coupled across said line, a said receiving
circuit coupled across said line, and a microprocessor,
means responsive to actuation of said operator's control of a sign
control unit at one location for activating the voltage source at
that location to cause the sign control unit at that location to
become a master unit and to deactivate the voltage sources at all
other locations to cause the sign control units at said other
locations to become slave units, said activated voltage source
being connected to said line as the sole source of excitation for
said line,
each transmitting circuit being adapted to place a low impedance
load across said line in correspondence with a binary data signal
input to said transmitting circuit, to modulate the voltage across
said line between a high voltage level and a low voltage level,
said levels representing and corresponding to binary data bits of
said input signal, and
each said receiving circuit including means for receiving said
modulated voltage from said line and deriving therefrom a binary
data signal,
whereby said master unit may communicate with each of said slave
units by modulating the voltage on said line by the master
transmitting circuit, and each slave unit may communicate with said
receiver circuits by modulating the voltage on said line by its
respective transmitting circuit.
8. A system as in claim 2 wherein each said receiving circuit
comprises a zener diode having a regulating voltage and connected
between the wires of said line, the regulating voltage of said
zener diode being greater than the voltage at any receiving circuit
caused by the maximum resistive volt-drop in said line between said
voltage source and receiving circuit when said shunt is across said
line and less than the voltage at any receiving circuit in the
absence of placing said low impedance shunt across said line.
9. A communication system comprising
a transmitting circuit,
a receiving circuit,
a two-wire line connecting said circuits,
a single voltage source connected across said line for supplying
voltage to said line,
means for transmitting from said transmitting circuit to said
receiving circuit binary information in the form of a sequence of
binary bits of two types representing marks and spaces of a binary
signal, comprising means at said transmitting circuit for applying
a low impedance shunt across said line to reduce the voltage at
said receiving circuit in correspondence with each occurrence of a
bit of said binary information of one type,
said voltage source having means maintaining both a substantially
uniform voltage for loads across said line having a range of
impedances greater than said low impedance and a substantially
constant current for loads across said line having a range of
impedances substantially equal to or less than said low
impedance.
10. A system as in claim 9 wherein said receiving circuit includes
an input having a zener diode connected across said line, said
diode having a regulating voltage at least as large as the voltage
at said receiving circuit caused by the resistive volt-drop in said
line between said transmitting and receiving circuits during
application of said shunt, said regulating voltage also being less
than that of said voltage source, whereby said diode will conduct
only in the absence of application of said low impedance shunt.
11. A method of communicating among units spaced along a continuous
two-wire conductive line, where each unit has a transmitter and a
receiver connected to said line, comprising the steps of
applying to said line a voltage source having a substantially
constant-voltage variable-current mode for currents up to a
predetermined current limit and a substantially constant-current
mode for a current in excess of said limit, and
transferring between said constant-voltage mode and said
constant-current mode in correspondence with a binary signal.
12. A method as in claim 11 further including
applying said voltage source at a single point along said line,
said source being the only power source on said line, and
causing said transferring by action of any of said
transmitters.
13. In a control system for trains having a plurality of cars, each
having a continuous conductive trainline extending from one end of
the car to the other end of the car, a power supply circuit for
supplying power to said train line, a car ground, a transmitting
circuit, and a receiving circuit, with each of said transmitting
and receiving circuits connected to said trainline to receive power
from the trainline, the combination comprising,
a first means for activating a car to become a master car,
means operative upon activation of a master car for connecting the
car ground of said master car to said trainline and disconnecting
all other car grounds from said trainline,
and means isolating the non-master receiving and transmitting
circuits from the grounds of their respective cars.
14. A system as in claim 13 including
one or more controllable display devices at each car,
means causing the master transmitting circuit to shunt a low
impedance load across said line in correspondence with a control
signal for controlling said devices, and
means at each receiving circuit for responding to such shunting for
controlling the display devices at the respective car.
15. A system as in claim 13, including means at each car to cause
it to become the master car in substitution for a previous master
car regardless of its position in the train.
16. A method of communicating in trains having a plurality of cars
and a two-wire trainline extending continuously from car to car,
each car having a unidirectional power supply circuit adapted to be
connected to said line to supply power thereto, a transmitting
circuit, a receiving circuit, and a car ground, with each of said
transmitting and receiving circuits being connected to the train
line in its respective car to derive power therefrom, the steps
of:
connecting the power supply circuit of one car to said train line,
and
concurrently disconnecting the power supply circuits of all other
cars from the train line.
17. The method as in claim 16, wherein each car also has a display
device, and including the steps of
causing the transmitting circuit of one car to shunt a low
resistive impedance across said train line in correspondence with a
signal,
causing at least one receiving circuit to respond to such shunting,
and
controlling by said one receiving circuit the display device at
such receiving circuit.
18. A method as in claim 16, including the steps of
causing a different car from said one car to have its power supply
circuit connected to said train line, and
concurrently disconnecting the power supply circuit and ground of
said one car from said train line.
19. A method as in claim 18 further including the steps of
causing one transmitting circuit to apply to the train line a first
voltage representing a first type binary bit of a coded binary a
digital signal to be transmitted,
causing said transmitting circuit to apply a low impedance across
the train line to change the voltage on the train line from said
first voltage to a lower voltage representing a second type of
binary bit of said signal, and
causing the receiving circuit in each car to respond to said first
and lower voltages to receive said signal.
20. A method as in claim 19 further including the step of
causing a different car from said one car to have its supply
circuit and ground connected to said train line, and
concurrently disconnecting the supply circuit and ground of said
one car from said train line.
21. A communication system for a multi-car train comprising
a plurality of spatially separated units, each unit comprising
(a) a communication line section consisting of two continuous
galvanically conductive wires, the line section of each unit being
galvanically connected serially to the line sections of all other
units to form a single two-wire line for all units,
(b) a transmitting circuit, and
(c) a receiving circuit,
each of said transmitting circuits and receiving circuits being
connected in parallel across said line at its respective location
whereby all said circuits are connected directly to said two
wires,
a single direct voltage source connected across said line at one
point thereof and providing the only source of voltage on said
line,
each transmitting circuit comprising means for causing the voltage
on said line produced by said voltage source to vary at all points
along said line between a high level and a low level in
correspondence with a binary signal to be transmitted,
each of said units being in a separate train car, and said two-wire
line extending serially from car to car along said train from one
end of the train to the other,
each car of the train having a said transmitter and a said
receiver, said voltage source being coupled across said line at a
selected (master) car, said line having no other voltage or power
sources connected to said line,
said voltage-varying means comprising means at each transmitter to
apply a shunt to said line in accordance with one bit of a binary
signal to increase the current in said line from said voltage
source and to reduce the voltage across said line at the receivers
of all cars during such shunting, and
each receiver having means to respond to said voltage reduction to
detect said signal.
22. A communication system comprising
a plurality of spatially separated units, each unit comprising
(a) a communication line section consisting of two continuous
galvanically conductive wires, the line section of each unit being
galvanically connected serially to the line sections of all other
units to form a single two-wire line for all units,
(b) a transmitting circuit, and
(c) a receiving circuit, and
(d) a direct voltage source,
each of said transmitting circuits and receiving circuits being
connected in parallel across said line at its respective location
whereby all said circuits are connected directly to said two
wires,
a single one of said voltage sources being connected across said
line at one point thereof and providing the only source of voltage
on said line,
each transmitting circuit comprising means for causing the voltage
on said line produced by said voltage source to vary at all points
along said line between a high level and a low level in
correspondence with a binary signal to be transmitted,
all said receiving circuits being adapted to respond to variation
of voltage on said line caused by a transmitting circuit of one
unit, to reproduce said signal,
and means assuring that at any time only a selectable one of said
voltage sources is connected to said line and that all other
voltage sources are concurrently disconnected from said line.
23. A communication system comprising
a plurality of spatially separated units, each unit comprising
(a) a communication line section consisting of two continuous
galvanically conductive wires, the line section of each unit being
galvanically connected serially to the line sections of all other
units to form a single two-wire line for all units,
(b) a transmitting circuit,
(c) a receiving circuit, and
(d) a ground
each of said transmitting circuits and receiving circuits being
connected in parallel across said line at its respective location
whereby all said circuits are connected directly to said two
wires,
a single direct voltage source connected across said line at one
point thereof and providing the only source of voltage on said
line,
each transmitting circuit comprising means for causing the voltage
on said line produced by said voltage source to vary at all points
along said line between a high level and a low level in
correspondence with a binary signal to be transmitted,
all said receiving circuits being adapted to respond to variation
of voltage on said line caused by a transmitting circuit of one
unit, to reproduce said signal,
and means assuring that at any time only a selectable one of said
grounds is connected to one wire of said line and that all other
grounds are disconnected from said line.
24. A communicating system for a plurality of spatially separated
units,
said units being interconnected only by a single line formed of two
continuously conductive wires,
each unit comprising (a) a voltage supply circuit adapted to supply
voltage to said line, (b) a transmitting circuit, and (c) a
receiving circuit,
the transmitting circuit and receiving circuit of each unit being
continuously connected across said two-wire line,
means at each unit for causing its voltage supply circuit to be
connected across said line, and
means operative upon connection of one voltage supply circuit to
said line for causing the voltage supply circuit of all other units
to be disconnected from said line, whereby said entire line is
supplied from only one voltage supply circuit at any time.
25. A system as in claim 24 wherein each said voltage supply
circuit includes a ground adapted to be connected to one of said
line wires, whereby said line is provided with a ground from only
one voltage supply circuit,
each of said transmitting and receiving circuits being provided
with a ground only by said line.
26. A system as in claim 25 including isolating means for isolating
each transmitting circuit output and receiving circuit input
connected to said line from other circuits in their respective
units.
27. A train communication system having cars of the train connected
directly by a two-wire train line running continuously and
conductively from car to car, each car having a power source, a
receiver and a transmitter comprising:
means for causing any car to be a master unit and for concurrently
disconnecting the power sources of all of the other cars from said
train line, leaving the master unit power source as the sole power
source for the line,
means for causing the master unit to apply to said line a high
voltage representing a binary bit of a first type of a binary
digital signal to be transmitted,
the transmitter in each car being coupled to said train line and
being adapted to apply a low impedance across the train line to
change the voltage on the train line from a value representing said
first type bit to a lower value representing a second type binary
bit, in correspondence with said binary digital signal,
the receiver in each car being coupled to said train line and being
adapted to receive said signal.
28. A message display system comprising:
a plurality of message display devices,
a two-wire communication line,
a plurality of sign control units, each at a different location,
and each associated with one or more of said display devices at a
respective location, said sign control units being connected to one
another solely by said two-wire communication line,
each sign control unit comprising a voltage supply whose output is
coupled across said line, an operator's control, a transmitting
circuit whose output is coupled across said line, a receiving
circuit whose input is coupled across said line, and a
microprocessor,
means responsive to actuation of said operator's control at one
location for causing the microprocessor at said location to
activate the voltage supply at that location to cause the sign
control unit at that location to become a master unit and to
disconnect the voltage supplies at all other locations from said
line to cause the sign control units at said other locations to
become slave units, said activated voltage supply being connected
to said communication line as the sole source of power for said
line.
29. A system as in claim 28, each transmitting circuit being
adapted to place a low impedance load across said communication
line in correspondence with a binary data signal input to said
transmitting circuit, to modulate the voltage across said
communication line between a high voltage level and a low voltage
level, said levels representing and corresponding to respective
binary mark and space bits of said input signal,
each said receiving circuit including means for receiving said high
and low voltage levels from said communication line and deriving
therefrom said binary data signal,
whereby said master unit may communicate with each of said slave
units by modulating the voltage on said communication line by the
master transmitting circuit, and each slave unit may communicate
with said receiving circuits by modulating the voltage on said line
by the slave transmitting circuit.
30. A communication system comprising
plurality of spatially separated units, each unit comprising
(a) a communication line section consisting of two continuous
galvanically conductive wires, the line section of each unit being
galvanically connected to the line sections of all other units to
form a single two-wire line for all units,
(b) a transmitting circuit, and
(c) a receiving circuit,
each of said transmitting circuits and receiving circuits being
connected in parallel across said line at its respective location
whereby all said circuits are connected directly to said two
wires,
a single direct voltage source connected across said line at one
point thereof and providing the only source of voltage on said
line,
each transmitting circuit comprising means for causing the voltage
on said line produced by said voltage source to vary at all points
along said line between a high level and a low level in
correspondence with a binary signal to be transmitted,
all said receiving circuits being adapted to respond to variation
of voltage on said line caused by a transmitting circuit of one
unit, to reproduce said signal.
Description
FIELD OF THE INVENTION
The present invention relates to systems for controlling multiple
devices, such as signs for displaying messages, as for highway
traffic control systems or for display of destinations in a number
of subway or railway cars. It is particularly described with
respect to a system for controlling and determining the display of
messages on each car of a multi-car train.
BACKGROUND OF THE INVENTION
In train systems such as subways, typically up to a dozen cars may
be coupled together at a terminal, the cars being selected from a
large pool of available cars. In some situations, the cars may be
kept joined in pairs, which are assembled into a train.
(Hereinbelow "car" shall refer to either a single car or a car-pair
treated as a single car.) It is desirable that a system be provided
for displaying the destination (or other message) on controllable
signs in each car, under control from one point of the train. For
desired flexibility, that control point should be available at any
car of the train.
For enhanced versatility and flexibility in display of messages, it
is desirable that such signs be electronic-controlled displays,
such as have been used in electronic bus destination signs, of
which one form is known as the Luminator or MAX Information Display
System. In such a system a library of different messages may be
stored in a memory, to be selected by an operator, for display on
one or more signs such as in the front, side or rear of a bus. Such
a system and a memory transfer unit for it is described in U.S.
Pat. No. 4,586,157 dated Apr. 29, 1986 and assigned to the assignee
of the present application. The present invention provides a system
useful to control a multiplicity of such displays, such as the
signs on the cars of a train or the signs of a highway traffic
control system or the like.
One problem associated with subway or other electric trains is that
each car has its own DC power source (as from third-rail or
overhead wires or other DC power supply) and has its own ground.
These grounds are separated by various and usually indeterminate
impedances. When interconnecting cars with a communication line,
differing voltage drops between the grounds of different cars may
create undesirable "ground loops".
This is avoided by the present communication system in which at any
one time power and ground are applied at only one car (a "master
car"), while all other cars are isolated from their normal ground
and power supply but utilize the power supply and ground of the
master car. Hence, there can be no potential difference between car
grounds, eliminating ground loops.
SUMMARY OF THE INVENTION
According to a feature of the invention, bi-directional data
communication is provided, between a "master" unit and all other
("slave") units, where any unit of the train may be made the master
unit, i.e., the master unit may be located anywhere along the train
and readily changed in location at any time by converting a former
slave unit to a master.
According to another feature of the present invention, each car of
a train system is provided with a set of message displays or signs,
and each car has its own sign control unit ("SCU"). In a multi-car
train, for example, an operator may make any one of the sign
control units a "master" unit, for determining the operation of all
of the sign control units of the other cars, which may be deemed
"slave" units. Each car (whether master or slave unit) has its own
data handling apparatus, including a message memory and
microprocessor for supplying a selected message from the memory to
the signs, to display the selected messages. Control over what is
displayed and the manner of display is centralized in the master
unit.
According to yet another feature of the present invention, control
from the master unit to the slave units and communication in both
directions between the slave units and the master unit, are
provided by causing all units to be directly coupled to the same
two-wire pair (called a communication line or trainline). Such a
line extends along each car, from one end to the other, both ends
being unterminated and open. Thus, the trainline runs in series
from car to car, and the trainline in each car is automatically
joined to the next car's line when cars are mechanically coupled to
one another. The trainline wire pair is not closed or terminated at
either end, permitting differing arrangements of individual cars to
be assembled as desired while maintaining the line extending the
length of the train. Circuits in each car are placed across the
line, in parallel fashion. Only the master unit controls electrical
data flow along the trainline, and losses and signal noise which
may be caused by circulating currents or voltage loops within a car
or between cars are avoided. The trainline is preferably a shielded
twisted pair to reduce noise pick up and cross talk in an
ordinarily high electrical/electromagnetic environment.
Communication is made in binary digital fashion, by modulating the
voltage appearing on the trainline, between a high value
representing one binary bit (e.g., logic "1" or a "mark") and a low
voltage value representing the other binary data bit (e.g., logic
"0" or a "space"). This modulating is produced at both master and
slave units by providing a normal high level voltage on the
trainline (from only the master unit) and shunting the trainline by
a low resistance (e.g., short circuiting the trainline) at the unit
transmitting data to provide a constant current, low voltage level.
The succession of high and low values then represent in digital
binary form the message data or control data passing between
units.
The present system also provides improved circuitry permitting
communication at a high baud rate (e.g., 19,200 minimum) between a
large number of units, up to a designed maximum, without degrading
the data signal. In contrast, prior trainline circuits have been
limited typically to the neighborhood of 1,000-1,200 baud.
The present invention provides particular circuitry and procedures
for a versatile and effective arrangement for controlling a
multiplicity of message displays from a single point, which may be
selectably located at any of the message display locations.
Further advantages and objects of the present invention will become
more apparent from the following description of a preferred
embodiment, taken in conjunction with the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan conceptual view of several cars of a train showing
the environment and general arrangement of the present
invention;
FIG. 2 is an enlarged partial view of FIG. 1 showing a coupler
between the cars of the train;
FIG. 3 is a schematic block diagram of one embodiment of the
invention showing a representative circuit of both a master sign
control unit and a slave sign control unit;
FIG. 4 is a circuit schematic of a voltage regulator and current
controller and a master/slave connect relay in accordance with the
invention;
FIG. 5 is a graphic representation of a typical output response of
the output voltage of a prior art regulator with respect to the
load across its output;
FIG. 6 is a graphic representation of the output response of the
voltage of a regulator in accordance with the invention, with
respect to the load across the output.
FIG. 7 is a circuit schematic of a data transmitter in accordance
with the invention;
FIG. 8 is a circuit schematic of a data receiver in accordance with
the invention;
FIG. 9 is a function diagram showing the operation procedure for
establishing which sign control units are active;
FIG. 10 is a status diagram showing the operation procedure for the
master microprocessor, for several purposes.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of the invention is intended for use with
trains, specifically electric subway-type trains, although usable
in other systems for controlling multiple signs or other devices.
The invention particularly provides improved communication between
and control of the display sign controllers of each car of the
train.
FIG. 1 shows some of the cars of an electric subway-type train 10.
Two cars are indicated as Car A and Car B. Cars A and B are
connected to each other, as are the remaining cars of the train 10,
through a coupling 12. The coupling 12 is a standard car-to-car
coupling intended to connect two abutting cars together, both
mechanically and electrically.
In accordance with the invention, a two-wire communication line
(trainline) 14 is provided along each car, to be interconnected
end-to-end between all the cars of the train 10. The communication
line 14 is represented in this figure as a single dashed line
through the center of the cars shown in FIG. 1, but will be
understood to be a shielded wire-pair, preferably twisted, to
minimize noise and cross-talk pickup from other circuits which may
be present in the same cable way, in the typically high electrical
noise environment and strong electromagnetic fields in such cars.
FIG. 2 shows an enlarged portion of the train 10 between two cars.
The two wires 14P, 14N of the communication line 14 of Car A, for
example, are automatically connected to the corresponding wires of
the counterpart communication line 14 of Car B when Cars A and B
are coupled together. All communication between the cars that
relates to the control and operation of the display signs within
each car in accordance with the invention is carried by the simple
two-wire communication line 14.
As shown in FIG. 1, each car of the train 10 includes a sign
control unit (SCU) 16, display signs 18, an operator's display
keyboard (ODK) 20 and a local power source 22 such as a 5-volt DC
power supply which may be part of the SCU. As indicated in FIG. 2,
the SCU 16 of each car of the train 10 includes a system processing
board (SPB) 24, a memory 56, a trainline interface board (TIB) 28
(which includes a microprocessor 54). Each SCU 16 also includes a
power supply board (PSB) 30 (which may include source 22) for
supplying the local power for the SCU for that car of the train
10.
The SPB 24 of the SCU 16 for a particular car is the display system
controller of that car. The TIB 28 of each SCU 16 interconnects all
of the SCUs 16 of the train 10, so that each SCU 16 can communicate
with the others, along the communication line 14. As described
later, any SCU 16 may be chosen to be a master SCU among all the
SCUs 16 of the train for controlling the display systems of the
entire train 10, by controlling the operation of all the remaining
SPBs which become slave SPBs.
Two or more display signs 18 are located at appropriate positions,
such as on either side of each car of the train 10, and are used to
display a message, either a preselected one from the memory 56 or
one inputted by an operator of the train 10 by using the ODK 20.
The display signs 18 are preferably of the LCD type, such as in the
Luminator MAX bus destination sign system, but any electronically
controlled sign can be used with the invention, such as those using
flip-dots or LEDs. The display signs 18 of each car are preferably
powered directly from the PSB 30 of that car of the train 10. The
control of signs 18 from SCU 16 may be accomplished in any desired
manner.
An operator at any car, by use of the ODK 20 located on that car of
the train 10, may communicate with the SCU 16 of that car, and
thereby control the message displayed by the signs 18 of that car.
In addition, by means of the TIBs 28 of all the cars connected to
the communication line 14, the display signs 18 of the entire train
10 become controllable by that ODK 20. The ODK 20 includes a
customary keyboard portion for command and data input and a display
portion to view the inputted data and the information currently
being displayed by the display signs 18. The ODK may be replaced by
any source of control signals for selecting particular messages to
display, such as a set of thumb wheel switches.
FIG. 3 shows a block schematic of a portion of a trainline
interface board (TIB) 28 and an SPB 24 (which may be contained in
microprocessor 54) of two separate SCUs 16, one SCU 16A of Car A
and the other SCU 16B of Car B. It will be understood that the Car
B slave unit is identical in circuit to the master unit of Car A,
although only partially shown in FIG. 3. Two display signs 18 are
controlled by the microprocessor 54 of each SCU 16, and an ODK 20
is an input thereto. As described below, the SCU 16 of one car may
be selected by its ODK 20 to have the status of "master", while the
other SCU 16 shown (and all other SCUs 16 of the train 10 not
shown) are then automatically placed in a "slave" status.
Referring to FIG. 3, train power at Car A is inputted by power
terminal 64 and car ground 62 to a voltage regulator and current
controller 40. Details of the regulator and current controller 40
are described below; it provides a regulated output voltage which
is substantially constant for current loads up to a predetermined
value, and toggles abruptly to a constant regulated current with
low voltage upon a very low resistance (high current) load. The
output of the regulator and current controller 40 is switched in or
out by a master/slave connect relay 42, which is in a closed
position for the master SCU 16A and in an open position for all the
slave SCUs 16, including SCU 16B, as discussed below. The
master/slave connect relay 42 under the control of microprocessor
54 connects the communication line wires 14P, 14N to the regulator
and current controller 40 or disconnects them from regulator 40.
Whenever the master/slave connect relay 42 is closed, its SCU 16
becomes the master SCU 16 (in FIG. 3, the master SCU 16 is SCU
16A), and the output of the regulator 40 in the master Car A (in
FIG. 3) is then directly connected to the communication line 14.
Power from the master regulator is thereby sent to all SCUs 16B
throughout the train 10, whose relays 42 are then kept open, so
that no power is drawn from the individual regulator 40 of any of
the slave SCUs 16B. The open relay 42 in each slave SCU 16B
electrically isolates the output of the slave unit regulator 40 and
the car power source 64, 62 of Car B (and all non-master other
cars) from the trainline 14.
The output of the master connect relay 42 is connected, as shown,
to trainline 14, one wire 14N of the trainline being a ground wire,
the other 14P a positive voltage wire. The ground for all of the
slave SCUs is then always the car ground 62 of only the master car,
Car A in FIG. 3, thereby avoiding ground loops.
In each car, connected across the train communication line 14 and
to the output terminals of the master/slave connect relay 42 is a
data transmitter circuit 44 and a data receiver circuit 46. The
data transmitter circuit 44 receives data from the SPB 24 (part of
microprocessor 54) of the car's SCU 16A.
The data to be transmitted by the master unit is used to modulate
the voltage supplied across the communication line 14 from the
master regulator 40 in such a manner that allows the data to be
sent along the communication line 14, with sufficient current for
operation of all the slave SCUs 16. As shown below, this is done by
rapidly shunting and unshunting the trainline 14 to create digital
signals representative of the data to be transmitted. The
transmitted modulated voltage operates the receiver components of
the slave SCUs, so that they may receive such data. They also may
transmit their own data to the master SCU 16A by a similar shunting
operation. The operation and a preferred circuit arrangement of the
transmitter circuit 44 are described in greater detail below.
The data receiver 46 of the each SCU 16 (including master SCU 16A)
is also connected across the line 14, and receives its input only
from line 14, independent of the local car power supply and ground.
Thus, the trainline remains connected to only a single power source
and ground (that of the master). The receiving circuit 46 receives
any modulated signals on the communication line 14 and transmits
them to microprocessor 54 which serves to control signs 18 by way
of sign processing board SPB of the microprocessor.
As described above, the master SCU 16A includes both the trainline
interface board (TIB) 28 and the sign processing board SPB 24. The
SPB 24 controls the operation of the TIB 28 and, if it is a master
SPB as in 24A, it also controls the operation of each TIB 28 and
microprocessor 54 in all the other cars of the train 10.
The SPB 24 includes a microprocessor unit (MPU) 54 and a memory
unit 56, each powered by the local power source 22. The
microprocessor 54 of the SPB 24 of each SCU 16 of each car of the
train 10 controls the related "local" functions of the particular
car; for example, the microprocessor of slave Car B controls the
display signs 18 located in Car B, the relay 42 of Car B and the
flow of data from Car B to the master SCU (Car A, for example). The
microprocessor 54 of the master SCU 16, however, controls the
individual microprocessors 54 of all other cars. The master unit's
microprocessor 54 only communicates serially through the trainline
14 to command the microprocessors of the slave units, but does not
directly control any functions in the slave units, which is
accomplished by the slave microprocessors. Communications from
master to slave are initiated only by the master, and
communications from slave to master (such as confirmations of
commands) are as permitted by the master, in a simplex-type
communication protocol, which puts data from only one unit on the
line 14 at a time.
Thus, the chosen master SCU 16A powers the entire communication
line 14, so that the data transmitter 44 and the data receiver 46
of each of the slave SCUs 16 operate with an isolated or floating
ground, which is that (62) of the master Car A. This arrangement
eliminates any problems associated with circulating currents such
as might be caused by output differences in the local car power
sources 64 of the different cars of the train 10. Such differences
in power source can lead to static and noise generation along the
communication line 14, often resulting in loss of data between SCUs
16. The load on the communications line 14 is kept small, limited
to the data transmitter and data receiver circuits of the several
SCUs, so that rise and fall times of the voltage are improved.
Local power is supplied to other circuits of the SCUs, from their
train power 64 or power source 22.
Referring to FIG. 4, a preferred circuit schematic for the
regulator and current limiter 40 and master/slave connect relay 42
is shown. Power is drawn from the car train power line 64. The
voltage at line 64 is preferably filtered, but not necessarily
regulated. The negative line 62 remains at car ground potential
while the positive line 64 is at a potential which illustratively
is of the order of 37 volts dc. A fuse 66 is preferably provided in
line with the positive line 64 to protect the entire trainline
circuit.
A light-emitting diode 70 and an appropriate series resister 68 are
connected across the input leads 62 and 64 to provide a "power-on"
indication for the trainline system. Zener diode 72 having a
regulating voltage illustratively of the order of 40 volts is
preferably connected across the power input leads 62, 64 to protect
the following circuitry from any voltage transients occurring in
the car power. One terminal of another zener diode 74 is connected
to the positive line 64 through resister 76 defining a node 78, the
other terminal of zener diode 74 being connected to the ground line
62. The zener diode 74 is used to provide a regulated voltage of a
predetermined value, illustratively of the order of 15 volts dc. A
capacitor 79, connected between node 78 and the ground line 62 is
used to help eliminate any electrical noise within the circuit and
to maintain a substantially constant voltage.
A shunt regulator 80, which may be a commercially available part
(Texas Instrument's part No. TL 431, for example), includes three
terminals or leads, namely, a cathode input lead 82, which
connected to node 78, an output lead 84, and a reference terminal
or lead 88. A resistor 90 connects the reference lead 88 of the
shunt regulator to the output lead 86. A diode 92 is connected
between the positive power line 64 and the output lead 86 to
prevent any reverse bias voltage derived from the capacitance of
the communication line 14 from injuring the circuit, as during a
power failure or circuit interruption.
Element 94 represents a commercially available I.C. chip which
essentially includes a standard Darlington transistor (Texas
Instrument part No. TIP122). The base terminal 96 of chip 94 is
connected to node 78. The collector terminal 98 is connected
directly to the positive input lead 64. The emitter terminal 100 of
chip 94 is connected to the output lead 86 through resister 90. The
output lead 86, representing the output of the regulator and
current controller 40, is connected directly to an input lead 102
of the master/slave connect relay 42. The ground lead 62 is
connected directly to another input lead 104 of relay 42. Any
appropriate relay may be used in the circuit of the invention;
however, in this preferred embodiment, a double-pole, single-throw
relay 42 is used. When the relay 42 is activated (under control of
microprocessor 54), the lead 102 (positive output of the regulator
40) is switched to a positive output lead 106 (as shown in FIG. 4),
and simultaneously, the negative ground line 62 is connected to a
negative relay output lead 108. The positive relay output lead 106
is connected directly through an isolating diode 134 to the
positive side 14P of the communication line 14. The negative relay
output lead 108 is connected through an isolating diode 134 to the
ground side 14N of the communication line 14. When the master/slave
connect relay 42 is deactivated (or not energized), the positive
lead 102 from the regulator 40 is connected to a third relay lead
110 which is connected to the ground lead 62 through a resistor 112
and a light-emitting diode (LED) 114. The resulting flow of current
will light the LED 114 whenever the master/slave connect relay 42
is in its non-activated position, indicating that this SCU is in a
slave configuration. The fourth relay contact is not used in this
embodiment. The master/slave connect relay 42 therefore controls
whether power from the regulator and current controller 40 is sent
to the communication line 14, or alternatively to an indicator LED
114.
To activate the master/slave connect relay 42, a line 116 is
provided from the local power source 22 to the positive terminal
118 of the coil of the relay 42. The negative terminal 120 of the
coil of the relay 42 is connected to the collector terminal of a
transistor 122. A diode 124 is connected between the positive and
negative terminals of the coil of relay 42 for preventing any
adverse effects on the operation of the relay 42 due to any reverse
bias generated during deactivation of the relay coil. The emitter
of the transistor 122 is connected to the return 21 for source 22.
The base of the transistor 122 is connected to a node 126 through a
diode 128. Node 126 is connected to local power source 22 through a
resistor 130. Another diode 132 is connected between node 126 and
the relay control output line 133 of microprocessor 54 of the SPB
24. An appropriate signal from the microprocessor 54 activates the
transistor 122 which, in turn, controls the relay 42 by controlling
the flow of current through the coil of the relay 42. Diodes 128
and 132 are used to bias the transistor so that the relay 42 can be
activated precisely and quickly.
In operation of the regulator and current controller 40, the
Darlington transistor 94 will provide a current flow through the
resistor 90 to the output node 86. The voltage drop across the
resistor 90 appears between the leads 84 and 88 of the shunt
regulator 80. At a predetermined voltage drop across the resistor
90 (illustratively of the order of 2.5 volts) caused by a low
resistance load on line 14, the shunt regulator 80 will become
conductive between its leads 82, 84, which will change the bias on
base 96 of the transistor chip 94. The resulting control by the
shunt regulator 80 will then maintain a substantially fixed current
output regardless of the load across the output terminals (between
lead 86 and ground line 62). That current is designed to be
sufficient to supply the data receiver and data transmitter
circuits of the SCUs for all the cars.
The circuit is a series voltage regulator which uses a high speed
constant current limiting circuit. It regulates quickly to toggle
between the constant voltage mode and the constant current mode,
which constitutes the transition between a mark and space for coded
communication. This circuit is only used for communication. As
shown below, it supplies power (e.g., of the order of one watt) to
isolated sections at each data transmitter and data receiver
circuit, sufficient for communication between the desired numbers
of cars. Other circuitry in the system is supplied by local car
power sources and power supplies.
The present invention modulates the voltage across the
communication lines 14N, 14P by shunting these lines in a
controlled manner dictated by the transmitter circuit 44 (described
below) and corresponding to the data that is being transmitted. It
is important, for high rate of data flow, that the transition
between high and low voltage states (i.e., between mark and space)
be rapid and certain.
Ordinarily, the voltage across a circuit such as trainline 14 would
vary with load placed on the line, as shown in FIG. 5, where the
voltage varies substantially linearly with decreasing load
resistance and increasing current of the load. However in the
present system, slave units will be at varying distances along the
train from the master unit, depending upon which unit has been
caused to become the master and depending upon the location of the
particular slave unit which may be in communication with the
master. This provides differing resistances between the slave and
the master unit, depending upon the length of line and line
resistance between the then transmitting unit and the then
receiving unit, each of which may be at any car of the train.
Thus, if the trainline 14 were switched between an open circuit
voltage and even a full short-circuit at a slave unit to provide
binary-coded information to a master unit, (or vice versa) in a
conventional power supply the voltage at the receiving unit would
vary from full voltage at open circuit at the transmitting unit to
some different value on short circuit at the transmitting unit,
depending on which unit is transmitting and its distance from the
receiving unit. This produces an indeterminate voltage low at the
receiving unit, which may adversely affect reliability of
communication.
To avoid these effects and to assure that both the voltage high and
the voltage low are definitive, the present invention provides an
output voltage from voltage regulator 40 with a characteristic such
as shown in FIG. 6, which maintains a substantially uniform (or
only slightly declining) voltage output for increasing loads (and
current) up to a predesigned value, at which the circuit converts
to a regulated current circuit, maintaining substantially constant
current (as at X, FIG. 6). The result is an abrupt voltage drop.
Therefore, as the communication line 14 is shunted by a slave unit
anywhere along the line, the maximum line resistance is designed to
have a value less than that represented at point X of FIG. 6 so
that the voltage on the trainline, previously maintained at the
upper level Y, will drop sharply upon shunting of the line to a
voltage well below the level Z indicative of the desired voltage
"low" representing a space or logic 0. This characteristic is
provided by the circuitry described above with respect to the
voltage regulator 40 of FIG. 4. In this way, the two voltage states
("high" or "low") representing the logic "0" or logic "1" binary
data bits are more precisely determined and data is transmitted and
received with greater reliability. The result is data being
transmitted from a master SCU to the slave SCUs or conversely, in
the form of a clean binary data signal.
Referring to FIG. 7, a preferred circuit schematic of the
transmitter 44 is shown. As indicated above, the transmitter
circuit 44 is connected across the communication line wires 14N and
14P. A zener diode 140 is connected between the negative
communication line 14N and a node 147. A noise-reducing capacitor
144 is connected between the negative communication line 14N and
node 147. A diode 146 and a resistor 148 are connected in series
between node 147 and the positive communication line 14P. The
communication line 14 therefore passes current through resistor 148
and diode 146 to charge up capacitor 144 until it attains the
regulating voltage (zener voltage) of zener diode 140,
illustratively of the order of 13 volts. An isolating coupler 48
(preferably an opto-coupler 48 with a Darlington transistor I.C.
152, such as Texas Instruments part No. 6N139) is supplied with
power from local source 22 through resistor 156 to an input portion
of the coupler 48 by line 154 and is connected to the
microprocessor 54 by line 155. Data from the microprocessor 54 will
control the flow of current along line 154 and thereby control the
input to coupler 48. The chip 152 is powered by the voltage at node
147.
The coupler 48 forwards the data signal to a conventional schmitt
triggering circuit 162 illustratively in the form of an I.C. chip
such as Texas Instrument part No. CD40106B. The output of the
triggering circuit 162 is connected to a node 164 which is
connected to the gate 166 of a power mosfet 168. The drain 170 of
the mosfet 168 is connected directly to the positive communication
line 14P. The source 172 of the mosfet 168 is connected directly to
the negative communication line 14P. A zener diode 174 and a
parallel resistor 176 are connected between the negative
communication wire 14N and node 164. It is appreciated by those
skilled in the art that the schmitt triggering circuit 162, the
resistor 176 and the zener diode 174 are used to provide a more
effective pulse wave shape with sharp rise and fall, and hence
improved switching characteristics and operating performance for
the mosfet 168.
In operation of the transmitting circuit 44 and coupler 48, an
output voltage signal modulated by binary data representing
information to be sent over the communication line 14 is produced
by the transmitter circuit 44 in response to a pulsed signal sent
by the microprocessor 54 over lead 155. This modulating signal is
coupled through and amplified by the coupler 48 and trigger 162, to
operate the mosfet 168. The mosfet 168 will become conductive
between its leads 170, 172 in response to and corresponding with
the pulse modulating signal and will therefore modulate the voltage
across the communication lines 14N and 14P by repetitively shunting
the positive communication line 14 nearly to ground, which drops
the previous high line voltage to a low value during one of the
binary bits of the modulating signal.
Thus, according to the present invention, communication along the
trainline 14 is accomplished by transmitting data from master unit
to slave unit (or from slave unit to master unit) by controlling
the voltage on the trainline, by switching the line voltage from a
high value to a low value, each value corresponding to a logic "0"
or logic "1" bit of a binary data signal. This switching is
accomplished at either the master or any slave by applying a
substantially zero or low resistance load across the trainline 14
by power mosfet 168.
The voltage supplied to the communication line 14 from the master
unit is used by the slave SCUs 16 to provide power for the portion
of their transmitter circuits 44 coupled to communication line 14,
those portions being isolated from the remainder of the SCU by the
opto-couplers 148. Capacitor 144, diodes 140, 146 and resistor 148
of a slave unit serve to extract power from the voltage on line 14
so that the slave transmitter circuit 44 can return data to the
master SCU merely by shunting line 14, without drawing power from
its own regulator 40 (which is then cut off). While the line
voltage is "high", capacitor 144 is charged through resistor 148
and diode 146 until the voltage rating of zener diode 140 is
reached. When the line voltage is "low", because some unit is
transmitting data, the diode 146 prevents discharge of capacitor
144, which substantially retains its voltage to supply necessary
voltage for chip 152 and schmitt trigger 162. Any loss of charge is
replenished when the voltage of line 14 goes "high" again, which is
its rest condition as well as the condition for one of the logic
bits. Therefore, the data communication circuits of the slave SCUs
16 of the train 10 are effectively powered by a single regulated
voltage supply, that of the chosen master SCU 16.
In response to data or commands from the master unit, as controlled
by its microprocessor, one or more slave units addressed by the
master unit may respond by the transmit signal placed on its line
155, to produce binary-coded shunting of the line 14 by the slave
unit's mosfet 168. The master microprocessor determines which slave
unit transmits and when, by controlling the slave microprocessors
so that the master and slave units do not transmit
simultaneously.
All the data receiver circuits 46 of the various SCU's 16 in the
system are identical and each is connected across the communication
lines 14P, 14N. A preferred receiver circuit is shown schematically
in FIG. 8. The switched-voltage data signal on wires 14P, 14N is
supplied to an isolating coupler (e.g., an opto-coupler) 182
through resistor 186 and zener diode 184. The coupler 182 is also
preferably in the form of an I.C. chip and may be the same type of
I.C. chip as used in the transmitter circuit described above. The
portion of the coupler 182 not connected to wires 14N, 14P is
powered from the local car power source 22. An output lead 188 of
the coupler 182 is connected to the power supply 22 through a
resistor 190. A capacitor 192 is connected between the output lead
188 of the coupler 182 and the ground return 21 of the power source
22. A lead 194 of the coupler 182 is also connected to the ground
21. A resistor 196 is connected between terminal 187 of the coupler
182 and the ground 21. The coupler output is supplied to a schmitt
triggering circuit 198 similar to the one used in the transmitter
circuit described above, which is connected between the output lead
188 of the coupler 182 and a receiver circuit output terminal 200.
A pull up resistor 202 is connected between the circuit output
terminal 200 and the power source 22, which also energizes circuit
198 by lead 199. The output terminal 200 of the receiver circuit is
then connected to the microprocessor 54, which determines the use
to which the received data is to be put (e.g., to acknowledge
receipt of signals transmitted from the master unit, or to supply
message data to the signs 18).
As is apparent to those skilled in the art, the schmitt triggering
circuit 198, the capacitor 192 and the resistor 196 are used to
filter and square-off the output data pulses. Also, the zener diode
184 and resistor 186 create a threshold voltage, several volts
above zero, below which the receiver will register a logic "0". The
regulating voltage of the zener 184 is selected to be just greater
than the voltage created at its receiver by the maximum volt drop
which may be experienced along the trainline (for example, if the
master is at one end of the train and a slave transmitter is at the
other end of the train seeking to communicate with the receiving
circuit at the master's location). Thus, so long as the trainline
voltage is high (for "mark") current will flow through zener 184
into the coupler 182 input. When the trainline voltage at a
receiver drops below its zener regulating voltage due to shunting
at any car, the zener 184 becomes non-conductive, cutting off input
to the opto-coupler, designating a "space", regardless of the
differing trainline resistances to the various cars. The circuit
thus defines the values of low and high voltage states so that
current will flow through the coupler 182 only when the voltage
detected along the communication line 14 exceeds a predetermined
value as dictated by the value of the zener diode 184.
Representatively, this may be about 6 volts.
The operation of the system is determined by the microprocessor 54
of the controlling (master) SCU 16 which controls the operation of
all the slave SCUs 16 by controlling the microprocessor 54 in each
slave SCU 16. The master microprocessor 54 uses the communication
line 14 to send data to and receive data from any or all the slave
SCUs, by following a specified software protocol as outlined in the
charts of FIGS. 9 and 10, described below.
Furthermore, the SCU 16 within each car controls each of its own
peripheral devices, such as the signs 18 and the ODK 20 within the
particular car. Through the use of the SPB portion of the SCU 16 of
each car, data flow is controlled between the SCU of the car and
the car's peripherals. The TIB portion of each SCU 16 allows the
master SCU 16 of the train 10 to interface with and determine the
action of all SCUs 16 together, as described above. FIG. 10 may be
taken as showing also the flow of data between the SCU 16 in each
car and that car's peripherals.
Customarily, each car for a train has a master switch (i.e.,
key-switch or forward/reverse switch) which first energizes the car
such as to turn on the headlights of the car when it is a lead car.
When, for example, ten train cars are connected to form a train 10,
the key switch which is first activated creates a voltage which is
detected by and informs the microprocessor 54 of the SCU 16 in that
car to activate its master/slave connect relay 42, thereby
connecting its power lines 62, 64 through its regulator 40 to the
communication line 14 common to it and the other nine cars of the
train 10. The connect relay 42 of all other (slave) cars is kept
de-energized (by command from the master CPU 54 to all slave CPUs
54), so that no slave unit power supply 40 is connected to the
communication line 14.
As a preliminary operation, the system first identifies which cars
are in the train. While all cars have the same sign control
equipment, each SCU (and thus each car) is assigned its own
permanent pre-programmed address which is unique, so that no two
cars have the same address. In the present arrangement, up to 2000
separate addresses may illustratively be used for up to 2000 cars,
without duplicating addresses. Of course, the number of possible
addresses may be increased, as desired, by appropriate choice of
the microprocessor used and its memory capacity. Each CPU 54 thus
will accept and respond only to messages or commands identified by
its own specific address.
FIG. 9 is a function diagram illustrating a preferred way in which
the master microprocessor 54 establishes which SCUs 16 (of the 2000
cars) form the particular train 10 so that it can then address them
and communicate with them as necessary, and in addition sets the
SCUs in proper condition. In order to save computing time and
memory space, a slave table 300 is generated and provides a current
list of address data designating those SCUs 16 that have been
recognized as being connected to form the train 10. The train table
300 is kept in non-volatile memory and is continually updated in
the search (i.e., polling) cycle indicated in FIG. 9. In the above
example, the table should contain ten SCU addresses (nine slaves
and one master).
First, by operation of its microprocessor 54, an SCU 16 becomes
master upon actuation of the key-switch (indicated at circle 301).
As indicated above, concurrently all other SCUs are conditioned to
become slaves. The microprocessor then resets a sequential counter
for the 2,000 addresses of the total number of SCUs (circle 312)
and then updates all the slave units listed in table 300, by the
procedure described below with respect to FIG. 10, to place them in
the "OK" state (starting by an "Idle" signal as described below).
In this update, each SCU listed in table 300 is interrogated; if
there is no response (because the address is that of an SCU not in
the train) that address is merely skipped.
The master microprocessor 54 then searches or polls through the
entire list of possible SCU addresses (in this example, 2000), but
not all at once. In order to provide prompt access to those SCUs
which are in the train 10, only a predetermined portion of the
total number, such as 250 addresses, is polled at a time. As
indicated by circle 302, the microprocessor 54 will call each
address of the first group and wait for a reply. If no reply is
received from an SCU at that address in a pre-determined time, then
it is assumed that no SCU exists in the train 10 with that address.
If any of the SCU addresses that do not reply are already listed in
the table 300, then these addresses will be removed from the table,
as indicated by circle 304, after which the poll continues to the
next address. If a reply is received by the microprocessor for a
particular address, then that address is added to the train table
300, as indicated in FIG. 9 by circle 306, again resuming to the
search (circle 302) when the addition is complete.
After a portion of the complete CPU list (e.g., after 250
addresses) is polled, the CPU 54 calls sequentially the SCUs 16
listed in the train table for a status check (indicated by circle
308). The status check procedure determines the status of the
particular SCU, for example, is it in an "OK" state, an "Empty"
state, a "Receive Configuration" state, etc., all described below.
The SCU is then put into or kept in the "OK" state. Thus, each time
the table is polled, all the SCU's listed in the table are placed
in the "OK" state, ready for further commands. As indicated by
arrow 310, after this checking the CPU 54 returns to the searching
procedure (circle 302) and continues with the next group (e.g., 250
addresses), followed by again checking the status of those SCUs
listed in the train table. This cycle (circle 308, arrow 310,
circle 302) is repeated until the full set of SCUs (all 2000 in
this case) has been polled, at which point the sequential address
counter is reset to zero (circle 312) to prepare for the next full
cycle.
By this cycle, the train table will list all SCUs in the train, and
each SCU has been placed in "OK" status. If during this cycle, at
circle 308, an ODK input is sensed at the master SCU addressed, the
message data called for by that input is supplied to all SCUs in
the manner described as to FIG. 10. This causes all the signs to
display the data called for by the ODK input. The searching at 308
then continues.
If during the status check (circle 308) a slave SCU is addressed
which has an input to its ODK, this is taken as an instruction to
take over mastership. The previous master is made a slave, as at
circle 307 (by switching off its voltage supply as described below)
and the former slave SCU becomes the new master. As indicated by
line 304, the new master enters the state shown in circle 301, and
the process described above is repeated.
After resetting the address counter (circle 312), the new master
CPU 54 then communicates with those SCUs whose addresses are listed
in the table 300, which are thus the only SCU's of the possible
2000, for example, that are in the particular train arrangement.
The SCU's listed in the train table are then updated (circle 314)
with the current display sign information and/or checked to make
sure that all signs of the train are displaying the proper message,
with for example, appropriate configuration parameters, destination
information, or the like to ensure that all display signs 18 of the
train 10 display the correct message.
This polling of the full set of SCUs is done continuously, at a
repetitive period of about 30 seconds. Thus regardless of whether
any car is replaced, or if the train is reassembled with different
cars, the train table is promptly made up and kept current. The
train table is thus continuously updated to ensure that the master
CPU 54 may correctly communicate with all the particular SCUs 16
present on the train 10. During each train polling cycle, (circle
302) the master CPU 54 will also check the status of the master ODK
and of the slave units to determine whether any change is needed in
the data determining the displays of the car signs of all cars. If
the master ODK 20 has data, indicating a message change (as
indicated by line 316), the new message will be transferred to all
signs by a command to all the SCUs 16 of the train table, as
described below.
Once the master CPU 54 has created an updated train table from
available SCU 16 addresses, communication with all or any SCUs 16
in the train can be performed according to the procedures outlined
in the chart shown in FIG. 10, while FIG. 10 is described in terms
of control of peripherals (e.g., signs) from the SPB of an SCU
(whether slave or master) it also illustrates the states of a slave
SCU in response to various commands from the master SCU. Thus, the
same diagram indicates the states of slave peripherals (e.g.,
signs) in response to commands from the SPB of each SCU 16 as well
as the states of slave SCUs in response to commands from a master
SCU.
Referring to FIG. 10, once the power of each car is turned on,
after coupling the cars into a train to interconnect their
trainlines 14, each peripheral of each slave SCU will be at an
"Empty" condition, as indicated by condition circle 320 of FIG. 10.
Depending on the type of sign used, the sign will either display
nothing (a blank screen) or its last message prior to being turned
off. With respect to each car of the train, the SPB of the SCU 16
will send a particular command such as a "Receive Configuration"
command, indicated by the command arrow 322 to a display sign
address stored in memory. The display sign 18 on that car at that
address will assume a "Receive Configuration" condition (circle
324) which will be detected by the SPB portion of the car SCU as it
polls its peripherals (i.e., signs 18 and the car's ODK 20) and
which will indicate to the SCU 16 that the particular display sign
is ready to receive general configuration data (such as length of
the message, font type, etc.). The actual configuration data is
then sent by the car SCU to the signs in turn, in a standard record
format (e.g., 16 bytes per record) which includes a data terminator
record, indicating the end of the particular data transmission. If
any errors occur, as suggested by the circle 326 (labeled
"Configuration Error"), as detected by a known check-sum method,
the "Configuration Error" will be detected during polling by the
SCU 16, and the configuration data will be re-sent, indicated by
command arrow 328. If no errors occur and the peripheral display
sign 18 successfully receives both the configuration data and the
appropriate data terminator, the peripheral will enter into a "Need
Data" state, indicated by circle 330, which, when read by the SPB
of the SCU will indicate a request for legend data from memory.
The SPB of the SCU will then prepare to send the legend data to the
sign by first sending a "Receive Data" command, command arrow 332
(meaning "are you ready to receive sign data?") to the particular
peripheral display sign 18. The peripheral will place itself into a
"Receive Data" condition (circle 334), which will indicate to the
SPB (as detected during polling) that the peripheral is ready to
receive data. Actual message data (representing the legend to be
displayed by the signs 18) is then sent and again includes a data
terminator record which is checked following the check sum
procedure used before.
If there are "Data Errors", either as to the data or the terminator
for data, as indicated by arrow 336, and the correct data transfer
is incorrect or incomplete, the peripheral display sign 18 will
enter a "Data Error" condition (circle 338). The "Data Error"
condition will be received by the SCU 16, which will repeat the
"Receive Data" command (command arrow 340, asking the peripheral
"are you ready to try again?"). When no errors result and the
entire legend data and data terminator record are received by the
peripheral 18 (indicated by arrow 342) the peripheral enters into a
"Wait Trigger" condition (circle 344), indicating to the SCU 16
that the peripheral 18 has received all the information sent and is
ready (upon command from the SCU) to display the stored legend
data.
At the appropriate time, the SPB of the SCU 16 sends a "Universal
Trigger" command (command arrow 346) which will cause the
peripheral 18 to display the message, placing the peripheral into
an "OK" condition (circle 348). The "OK" condition is read by the
SPB of the SCU 16, indicating that the display signs 18 are now
displaying the desired message. The SCU 16 may change the message
displayed by sending a new "Receive Data" command, to any
particular peripheral 18 (command arrow 350), placing the status of
the particular peripheral back to condition circle 340, and ready
to receive new data.
If the message to be displayed is longer than the display sign 18
can accommodate (e.g., is a multi-line message), the sign will
display a portion of the message in the "OK" condition (circle 348)
which will indicate to the SCU to change the status of the
peripheral to a "Need Partial Data" condition, needing another part
of the message (circle 354). While in the "Need Partial Data"
condition (circle 354), the display signs 18 will continue to
display the previous message (partial data) until overridden by new
data. The "Need Partial Data" condition 354 will be detected by the
SCU, causing the SCU to send a new "Receive Data" command (command
arrow 356), to the peripheral, placing the peripheral back to the
"Receive Data" condition (circle 340). New data is sent, as before,
during the "Receive Data" condition, again placing the peripheral
into the "Wait Trigger" condition. The "Universal Trigger" command
is sent after detection of the "Wait Trigger" condition signal,
again placing the peripheral 18 into the "OK" condition so that the
peripheral display sign 18 displays the message portion
corresponding to the new data.
While the display signs 18 are operating, the SCU can initiate an
"Idle" command, represented by command arrow 358, which changes the
status of the peripherals from the "OK" condition 348 to an "Idle"
condition (circle 360). This "Idle" command can be initiated during
any condition except the empty condition (circle 320). The "Idle"
condition functions as a pause control. The display sign 18 may
continue to display the previous message, but all activity (data
transfer) will cease, until a "Resume" command (arrow 362) is
issued by the SCU 16. While in the "Idle" condition, a "Reset"
command (arrow 364) can be sent to the peripherals 18 to reset
their current condition back to "Empty" (circle 320).
As stated above, the operation of the SCU 16 of each car of the
train 10 is controlled by the master SCU in one of the cars. The
master SCU 16 communicates along the communication line 14 to the
other SCUs 16 following the same process described and shown with
respect to FIG. 10. In this instance, the master SCU functions in
the same manner as the car SCU as described as to FIG. 10, and the
car SCUs function in the same manner as the sign peripherals. In
effect the master SCU of the train functions in the same way as the
described operations of the controlling SPB of the slave SCU. For
example, if the master SCU 16 has data to send to a particular
slave SCU listed in the slave table 300, it will send a "Receive
Configuration" command, as described above, to the particular slave
SCU (then in the "Empty" state). The slave SCU will change its
state to the "Receive Configuration" (circle 324 of FIG. 10). The
new condition will be detected by a confirmation signal returned to
the master SCU 16. As described above, configuration data will be
sent to the slave SCU 16. The SCU 16 enters a "Need Data"
condition, then a "Receive Data" condition after the master SCU
sends a Receive Data command (arrow 332). Again legend data will be
sent to the particular SCU 16 which will place it in the "Wait
Trigger" condition with the legend stored. Once the SCU 16 with its
stored legend message receives the "Universal Trigger" command, it
will proceed to communicate with its own peripherals, the display
signs 18, (as described above) following its own address order, as
if it were the master SCU for its own car.
In any slave car, if an operator introduces data on the car's ODK
20, this is taken as a demand to take over mastership, and for the
relays 42 of the requesting car and the previous master car to
interchange states, so that the new master will provide the sole
power for the trainline, as described above. The new master ODK 20
will enter a "Have Data" condition (circle 366) which will be
detected by the car's SCU 16 during its polling procedure of its
peripherals. Thus SCU 16 will request the new data by sending a
"Send Data" command (arrow 368) placing the peripheral ODK 20 into
a "Send Data" condition. Data will then be transmitted to the SPB
of the SCU 16 in the form of data records (e.g. 16 bytes per
record). After each record sent, the ODK 20 will enter a "Wait
Acknowledge" condition (circle 374) to wait for the SPB to continue
the transmission by sending a "Continue Send Data" command (arrow
376). If there are errors during transmission, the SCU will
automatically send another "Send Data" command (arrow 377) to
restart the transmission. Once the SPB of the SCU receives all the
new data from the ODK 20, it will enter a "Have Data" condition
with respect to the entire trainline which will be detected by the
master SCU of the trainline during its polling of all the SCUs 16.
This will cause the slave SCUs (whose ODK has data) to request
mastership from the previous master SCU, and transfer mastership to
the SCU whose ODK has the new data. The SCU 16 with the new data,
now the new master SCU of the trainline, will then send the new
data to all the other SCUs 16 of the train 10 in the order that
they appear in the slave table 300 and simultaneously proceed to
pass the new data to its own peripherals within its car. After each
slave SCU 16 receives the new data from the new master SCU 16, it
will in turn proceed in a similar manner to pass on the new data to
its local peripherals, such as the car's display signs 18 and ODK
20.
In order for the master SCU 16 to display the new data received
from it's ODK 20, it must send an "Idle" command to the display
portion of the ODK 20, (arrow 378), thereby placing the ODK's
display into the "Idle" state (circle 360). A "Reset" command from
the SCU 16 will then put the ODK's display in the "Empty" state
from which it can proceed to reload the new data into the ODK's
display, so that the operator can view the decoded equivalent of
what he has inputted. After the ODK's display is in the "OK" state,
the local SCU (which is now the master SCU) will continue to
distribute message data to its other peripheral addresses, as they
appear in the SCU's memory.
SUMMARY OF OPERATION
In operation of the entire trainline system, upon initialization of
the master SCU 16 by actuation of the first key-switch car of the
train 10, the relay 42 of the master SCU 16 is activated and held
closed so that power from the output of voltage regulator and
current controller 40 is sent along the communication line 14 to
all the other SCUs 16 (slaves). The equivalent master/slave connect
relay 42 in the slave SCUs will be kept de-activated and therefore
the regulator 40 of each slave SCU 16 will remain isolated from the
communication line 14. When the master CPU 54 desires to send
commands or message data to any or all the slave SCUs 16, it sends
corresponding coded binary pulses representing the command or
message data to its transmitter circuit 44, which shunts the
voltage across the communication line 14 by a low resistance in
correspondence with the binary data, and thus transposes the same
binary data signals from the CPU 54 to the communication line 14 in
the form of a pulse-modulated voltage signal. The modulated signal
is sent to all the SCUs 16 of the train 10 and read by the receiver
portion of each slave SCU 16. If the address information of the
received signal includes the address of a particular slave SCU 16,
then the data will be accepted and processed by the CPU 54 that SCU
16. Other SCUs 16 will ignore that signal. The addressed SCU 16
will follow the commands of the data in accordance with the
procedure described above and will communicate with and control the
display signs 18 and ODK 20 of its car, as necessary, until the
commands are complete. During the communication procedure,
acknowledgement or confirmation responses from the polled slave SCU
16 are provided by causing its mosfet 168 (FIG. 7) to short the
communication line 14 in an appropriate binary coded manner. The
voltage change thus produced is read by the master circuit's
receiver (FIG. 8), as described. Any car may become the master unit
by actuation of its ODK.
If an operator, located in a non-master (slave) car of the train
10, desires to change the message to be displayed by the signs
located in the cars of the train, he may do so through that car's
ODK 20. The new message will be detected by the slave CPU 54 during
its continuing polling procedure and will send a "request to become
master" to the pre-existing master CPU 54. The existing master CPU
54 will exchange mastership by deactivating its master/slave
connect relay 42, and immediately causing the requesting slave CPU
54 to activate its own master/slave connect relay 42 and become the
master SCU 16 of the entire train 10. The inputted message from the
actuated ODK 20 is then displayed by the display signs 18 of all
cars, as described above.
One advantage of the present system is that the data signal is not
degraded by the numbers of slaves in the system (up to the designed
maximum). This is because the voltage regulator 40 has a relatively
low output impedance and is in the constant voltage state when all
receivers are high (quiescent or mark state). This is in contrast
to conventional train systems which utilize a much higher impedance
voltage source, whose voltage drops by an appreciable amount as the
load of each receiving load is added to the system in increasing
the number of slave units accommodated.
Moreover, a quick transition is provided from a low voltage (space)
state to a high voltage (mark) state. This is created by having the
regulator in a constant current state during the spaces. Upon
change to the mark state, this causes charging of the line
capacitor linearly (rather than exponentially as is conventional
for high impedance sources), resulting in faster transition,
permitting higher baud rates. This also permits handling higher
resistance in the trainline wires or their couplings between cars,
and hence, more slave units.
The quick transition from high to low states uses a power mosfet as
the shunting device. Such a mosfet is fast in transition from no
conduction to full conduction, and can quickly shunt a large amount
of current with a high current rating. It also has low gate current
requirements, suitable for drive from a voltage source powering the
trainline.
Another feature is the use for the trainline of an unterminated
non-closed wire pair, aiding in the capability of having the master
anywhere along the trainline.
While the above system has been described primarily with respect to
providing controllable message displays or destination signs for
subway or train cars, it will be understood that the invention is
applicable to other systems having control of multiple message
displays or other devices. For example, in a highway traffic
control system or an airport message display system, message
display signs may be located at various points along the system,
which may be controlled from any sign location by use of the
present invention, with the various locations being interconnected
solely by a single wire pair. Other devices, such as car safety
devices or controls may also be made controllable from any selected
car.
It will be understood that the foregoing description is to be
deemed merely illustrative of the present inventions, which may
readily be varied or modified by those ordinarily skilled in the
art. The inventions shall be deemed defined solely by the appended
claims.
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